The present invention relates to adhesive bonding, and more particularly, to the bonding of surfaces wherein the control of bond line thickness and uniformity is desirable, as for example, in the packaging of semiconductor devices.
Reliable performance of electronic devices depends primarily on the integrity of the microelectronic components contained therein. Most electronic devices contain several microchips which are housed in a variety of protective packages. These protective packages often contain a variety of adhesive pastes which play an important role in maintaining the integrity of the package and thereby the performance of the microchip housed therein.
The recent production of electronic components containing microchips which are stacked one on top of another (commonly referred to as xe2x80x9cstacked diexe2x80x9d) presents challenges to the microelectronic packaging industry. For example, spacing between each die must be effectively controlled to allow for reliable wire bonding between die. Moreover, the recent trend toward thinner dies increases the propensity of the die to warp, resulting in non-planarity across the surface of the die (also a contributing factor to unreliable wire bonding). Thus, an adhesive used in a stacked die application ideally provides reproducible bond line thickness in addition to uniform planarity across the entire bondline.
In addition, interfacial stress that arises from a thermal mismatch between the die and substrate is directly proportional to both the area of attachment and the modulus of elasticity of the bonding adhesive. This stress is also inversely proportional to the bond line thickness. Since the modulus of elasticity for a given die attach adhesive is substantially fixed, alternative methods to reduce interfacial stress must be employed, e.g., via bond line control between a given set of components. If the bond line thickness is sufficient, the resultant bond will exhibit good resistance to differential thermal expansion rates between each semiconductor die and substrate and will produce a bond having a high tensile strength.
Accordingly, there is a need for effective methods to control bond line and planarity in the packaging of semiconductor devices.
In accordance with the present invention, there are provided adhesive compositions useful for effectively controlling bondline thickness and planarity. Invention adhesive compositions comprise at least one maleimide-containing monomer, optionally at least one cure initiator, and a plurality of spacers constructed from one or more organic polymers. Invention adhesive compositions are particularly useful for controlling bond line thickness and planarity between a device and a substrate, or between semiconductor dies in a stacked die package. Bond line thickness and planarity are largely determined by the size of the spacers in the adhesive composition.
In further aspects of the invention, there are provided methods for creating a substantially uniform bond line between a device and a substrate, for controlling adhesive gap thickness between a device and a substrate, for controlling planarity across an adhesive bond line, for creating substantially uniform bond lines between at least one semiconductor die attached to a substrate in a stacked arrangement, and for adhesively attaching at least two semiconductor dies to substrate in a stacked arrangement without the need for a spacer die.
In an additional aspect of the invention, there are provided assemblies comprising a first article adhered to a second article by a cured aliquot of invention adhesive composition.